Ministry of Earth Sciences
Forecast for the 2020 Southwest Monsoon Onset over Kerala
The monsoon onset over Kerala this year is likely to be on 5th June with a model error of ± 4 days
The National Weather Forecasting Centre of the India Meteorological Department,has come out with the forecast of Monsoon onset over Kerala. The silent features are given below:
This year, the onset of southwest monsoon over Kerala is likely to be slightly delayed as compared to normal date of onset of 1st June. The monsoon onset over Kerala this year is likely to be on 5th June with a model error of ± 4 days.
1. Background
Advance of the southwest monsoon over Indian main land is marked by monsoon onset overKerala and is an important indicator characterizing the transition from hot and dry season to a rainyseason. As the monsoon progresses northward, relief from scorching summer temperatures isexperienced over the areas. Southwest monsoon sets over Kerala on 1st June with a standarddeviation of about 7 days. India Meteorological Department  has been issuing operationalforecasts for the date of monsoon onset over Kerala from 2005 onwards. An indigenouslydeveloped state of the art statistical model with a model error of ± 4 days is used for the purpose.
The 6 Predictors used in the models are; i) Minimum Temperatures over North-west India, ii) Premonsoonrainfall peak over south Peninsula, iii) Outgoing Long wave Radiation  over southChina Sea,  Lower tropospheric zonal wind over southeast Indian Ocean,  upper troposphericzonal wind over the east equatorial Indian Ocean, and  Outgoing Long wave Radiation over the south-west Pacific region.
IMD’s operational forecasts of the date of monsoon onset over Kerala during the past 15
years  were proved to be correct except in 2015. Forecast verification for the recent 5years  is given in the table below.:
Year Actual Onset Date Forecast Onset Date
2015 5th June 30th May
2016 8th June 7th June
2017 30th May 30th May
2018 29th May 29th May
2019 8th June 6th June
2. Status of the 2020 Southwest Monsoon and Advance over the Andaman Sea
In the Indian monsoon region, initial monsoon rains are experienced over south Andaman Sea and the monsoon winds then advance in a north-westwards across the Bay of Bengal. As per the new normal dates of monsoon onset/progress, the southwest monsoon advances over the Andaman Sea around 22nd May. At present, a well-marked Low-Pressure Area lies over southeast Bay of Bengal & neighborhood. It is very likely to concentrate into a Depression over the same region during next 12 hours and further intensify into a Cyclonic Storm over central parts of south Bay of Bengal by 16th May evening. Associated with this event, conditions are likely to become favorable for advance of Southwest Monsoon into Andaman Sea, Andaman & Nicobar Islands and some parts of southeast Bay of Bengal, during next 48 hours. Past data suggest that there is no association of the date of monsoon advance over the Andaman Sea either with the date of monsoon onset over Kerala or with the seasonal monsoon rainfall over the country.
3. New Normal Dates of Onset/Progress and Withdrawal of Southwest Monsoon over India
India Meteorological Department  had released new normal dates of onset and withdrawal of southwest monsoon based on recent data in a press release dated 15th April 2020. The normal dates of onset are revised based on data during 1961-2019 and normal dates of withdrawal are revised based on data during 1971-2019. Now the detailed report  on the new normal dates of monsoon onset and withdrawal is ready and given in the below link.
http://www.imdpune.gov.in/Clim_Pred_LRF_New/Reports.html